This is a randomized, double-blind, 6 month-long treatment study comparing 40mg of alendronate, a new bisphosphonate, with 400mg of etidronate (Didrone) given daily in Paget's disease. End points will be decrease in serum alkaline phosphatase (and urinary hydroxyproline) and in a subset of patients - effects on bone histomorphometry (bone biopsy).